BACKGROUND AND OBJECTIVES: Pediatric spinal
anesthesia has gained popularity mainly as an alternative to general anesthesia
in pre-term neonates at risk for developing neonatal apnea. This study aimed
at evaluating anatomic, physiologic and pharmacological differences of the technique
in children.CONTENTS: Spinal anesthesia in children is being used since the early
20th century, but was overlooked for many years due to the introduction
of inhalational anesthetics and neuromuscular blockers. It regained popularity
in 1979. Its positive effects in pediatric anesthesia are cardiovascular stability
in children up to 8 years of age, satisfactory analgesia and muscle relaxation.
Most popular pediatric anesthetics are tetracaine and bupivacaine in doses adjusted
to body weight, but this technique is limited by a relatively short duration
of anesthesia. Surgical procedures cannot last more than 90 min and there is
no satisfactory postoperative pain control. Complications are the same for adult
patients and include post-dural puncture headache and transient radicular irritation.
Indications are: lower abdomen, genitalia, perineal region, lower limbs and,
in some cases, even thoracic surgeries. It is particularly attractive for pre-term
neonates at higher risk for postoperative apnea after general anesthesia.CONCLUSIONS: Spinal anesthesia in children is a relatively safe technique
with few complications and may be considered an alternative for general anesthesia,
especially for pre-term neonates at risk for postoperative respiratory complications.

The first report on pediatric spinal
anesthesia was published by August Bier in 18991, when the technique
was performed with cocaine in an 11-year old boy submitted to ischium abscess
drainage.

In 1900, Bainbridge2
reported 40 surgical procedures under spinal anesthesia, including a patient
under 3 months of age. In this case - strangulated inguinal hernia - the author
noted that the child would not survive a general anesthesia. In fact, this was
justified because by that time general anesthesia was induced with dripping
chloroform3.

The British surgeon Tyrell Gray
has published, in 19094, the results of a series of 300 pediatric
spinal anesthesias for procedures below the diaphragm. The author was impressed
with the low incidence of postoperative nausea and vomiting.

Several other reports on spinal
anesthesia were published by Junkin (1933)5, Robson (1936)6
and Berkowithz et al. (1951)7.

Leigh et al.8, in 1948,
have observed that all pediatric anesthesias in the Vancouver Hospital were
spinal. There is even a report on spinal anesthesia for more complex surgical
procedures, such as lobectomies and pneumectomies.

With the overall improvement of
general anesthesia, the introduction of neuromuscular blockers (1944) and of
modern inhalational anesthetics, starting with halothane in 1956, there was
a decrease in the use of spinal anesthesia3.

Gouveia9, in 1970,
has published his personal experience with this technique performed in 50 children
between 3 months and 12 years of age. The author has observed no complications.

Pediatric spinal anesthesia was
also considered safe by Cunto10 who, in 1975, has performed it in
84 children between 19 days and 13 years of age.

In 1984, Abajian et al.11
reported the use of spinal anesthesia in 78 children under one year of age,
36 being considered at high risk. These facts explain the rebirth of the technique.

Technological advances and better
training of neonatal intensive care units staff have increased the survival
rate of pre-term neonates often referred to anesthesiologists for inguinal hernia
correction. Spinal anesthesia has been proposed as the single anesthetic technique
with the aim of decreasing immediate postoperative apnea, which is high in this
group of patients depending on the post-conceptual age.

ANATOMIC CONSIDERATIONS

There are important anatomic differences
between children and adults, which are related to the child's development
stage which should be considered at spinal blockade induction.

Neonates spinal cord extends at
the level of the third lumbar vertebra (L3) and, at the end of the
first year of life reaches the location seen in adults, at the first lumbar
vertebra (L1)9,10,12-14.

Lumbar puncture in this age group
must be performed below the 4th or 5th lumbar vertebrae
(L4-L5 or L5-S1 interspace), for
additional safety due to the risk of reaching the spinal cord with the needle3,9,15. In plotting an imaginary line between neonate's iliac
crests, it will cross the spine at L4-L5 interspace, while
in the adult it will cross the spine at L3-L4 interspace16.

The spinal cord of a neonate weighing
3 to 4 kg is approximately 20 cm long, while in the adult it is 60 to 75 cm
long. So, the neonate spinal cord is, proportionally, 5 times longer as compared
to its weight than that of the adult11,16,17.

Another important factor is CSF
volume, which in the adult is 140 ml with 75 ml in the spinal space. In children,
total volume varies from 40 to 60 ml with half of it in the spinal space. So,
although a reduced total volume in children, the relative volume is higher (2
ml.kg-1 in adults and 4 ml.kg-1 in children)3,9,10,12-18.

Children's spinal cord is
highly vascularized allowing for a fast local anesthetic clearance11,14.

LOCAL ANESTHETICS

Esther-type local anesthetics (procaine,
tetracaine) are metabolized in the plasma by pseudocholinesterase. Neonates
and children up to 6 months of age have 50% of such enzyme as compared to adults.
Clearance may be decreased and local anesthetic effects may be prolonged, although
without clinical relevance12,19.

Amide-type local anesthetics (prilocaine,
lidocaine, bupivacaine, ropivacaine) are metabolized in the liver and show high
protein binding capacity. Liver blood flow is lower in neonates and children
under 3 months of age and metabolic mechanisms are immature. In addition, albumin
and a1 acid glycoprotein concentrations
are low, contributing to the increased concentration of free local anesthetics
and increasing the odds for toxic effects12,19-21.

The large balanced distribution
volume may give clinical protection by decreasing local anesthetics and other
drugs plasma concentration12,21,22.

A caveat must be done as to the
use of prilocaine in neonates. Its metabolism produces oxidants which may lead
to methemoglobinemia. Pre-term babies and neonates are more susceptible to such
complication for having, in different degrees, fetal hemoglobin (HbF) which,
only at 6 months of age is totally replaced by adult hemoglobin (HbA), more
easily oxidized, and low levels of methemoglobin redutase19,23.
Local eutectic anesthetic mixtures (LEAM) for venous or even spinal puncture
in neonates should be very carefully used.

Local anesthetic doses for children,
especially neonates, are higher than the corresponding doses for adults14,17.

Several anatomic aspects have already
been studied and may explain higher doses. As examples:

1. Higher CSF volumes (4 ml.kg-1)
could dilute injected local anesthetics14-16;2. Spine and spinal cord are longer than
in the adult as compared to body weight and the spine/body weight ratio in
children is five times that of the adult14,17.

The literature reports different
local anesthetics used for spinal anesthesia in children and tetracaine (0.2
to 0.6 mg.kg-1) is the most popular.

There are two local anesthetic
drugs commercially available in Brazil for this aim: lidocaine and bupivacaine9,10,12.

Table
I shows local anesthetics and their doses for pediatric spinal anesthesia.

PUNCTURE

Two anesthesiologists are needed
for this technique: one performing the puncture and the other positioning the
child and maintaining free airways. Most of the times there will be the need
for sedation or even anesthesia to perform the puncture, which may be done in
the lateral or sitting position. Head extension, especially in sedated or anesthetized
children, is mandatory due to the risk for hypoxemia14,15,18,30.

In the sitting position, reference
points are more easily identified and CSF will more easily flow due to higher
hydrostatic pressure18,19.

Puncture shall be performed between
L4-L5 or L5-S1 to avoid spinal cord
damage. Structures crossed by the needle are more difficult to identify12,16.
Most common needles are 24, 25 and 26G Quincke. The use of a mandrel prevents
epidermal cells to be carried to the neural axis, which may cause epidermoid
tumors11-13,15,16.

Spinal puncture in children is
more difficult than in adults. For better mastering such technique, training
should be performed first in adults, then in children and eventually in the
neonate. This way, the risk for complications is decreased.

Several authors have evaluated
spinal puncture difficulties in children and classified them as:

After puncture success confirmation
by CSF flow through the needle, local anesthesia is induced. It should be prepared
in syringes used for insulin with the exact dose to be injected11-13.

Distance from skin to dura must
be observed to prevent unnecessarily introducing the needle thus increasing
the odds for complications. Several reports have attempted to define this distance.
In practice, it is around 0.5 to 1 cm from the skin in the neonate and increases
with the development of the child10-12.

Local anesthetic injections have
received several recommendations. CSF aspiration before and after drug injection
to assure the correct positioning of the needle is recommended by some16
and not advised by others11. When CSF aspiration is the choice,
one must have in mind that the local anesthetic dose to be injected is low and
this procedure may dilute the agent in the CSF.

The administration of extra 0.04
ml of local anesthetics to compensate needle dead space is preconized by some
authors11,14.

Abajian et al.11 recommend
that the needle should not be removed immediately after local anesthetic injection;
it should be removed 5 to 10 seconds after injection to prevent local anesthetic
return through the puncture hole.

After needle removal, patient is
placed in the supine position. Motor block is installed in 1 to 2 minutes and
peak of analgesia is reached after 20 minutes32. Children should
not be manipulated soon after being placed in the supine position because some
authors have observed very high blockades caused by leg rising to position the
electrocautery plate3,9-11.

Spinal anesthesia duration in children
depends on the local anesthetics and its association with a vasoconstrictor.
However, literature and clinical practice have shown that this duration is of
approximately 90 minutes, which limits its use for longer surgeries16,18.
Tobias16 warns about practical criteria adopted by different studies
evaluating spinal anesthesia duration. Some define surgical anesthesia duration
as the end of anesthesia (surgical procedure's dermatome sensory block
duration), while others define it as motor function recovery. Some studies have
evaluated the addition of epinephrine to the spinal solution to increase anesthetic
blockade duration.

Gouveia9, in 1970,
has used 5% lidocaine in children from 3 months to 12 years of age and recommended
higher doses (2 mg.kg-1) in children up to 3 years of age and lower
doses (1 mg.kg-1) in older children. Mean blockade duration was 45
minutes and the association of a vasoconstrictor has not increased anesthesia
duration. However, Cunto10, in 1975, has used the same anesthetics
(5% lidocaine) in doses of 2, 3 and 4 mg.kg-1, with a maximum dose
of 100 mg. The increased dose and the association of a vasoconstrictor were
directly related to the increase in blockade duration.

Rice et al.32 have
noticed a longer tetracaine action from 86 ± 4 min to 128 ± 3.3 min
after epinephrine association to the spinal solution. Fosel et al.31
have also reported longer surgical anesthesia duration with bupivacaine associated
to epinephrine, from 50 to 90 minutes. This short local anesthetic duration
is explained by the increased absorption by a higher spinal cord vascularization
present in this age group11.

EFFECTS OF SPINAL ANESTHESIA
IN CHILDREN

Cardiovascular

The major advantage of spinal anesthesia
in children is the relative post-blockade cardiovascular stability. Differently
from adults, children have little or no heart rate and blood pressure changes4,10-12,15,35-37. Some authors predict this stability until 5 years
of age while others predict it until 8 years of age11,12,23.

Dohi et al.36 have shown
hemodynamic stability in children up to 5 years of age submitted to spinal anesthesia
with high sensory block (T2, T3) without previous hydration
or vasoactive drugs. Above 6 years of age there has been a mild decrease in
blood pressure and between 8 and 15 years of age there has been a more marked
blood pressure change.

Spinal blocks reaching the cervical
segment have been induced for ductus arteriosus patency correction in neonates
without previous hydration and with minor blood pressure changes35.
Several authors have found similar hemodynamic stability in neonates or infants
up to one year of age9-11,18,35-37.

Factors involved in this extraordinary
hemodynamic stability are still not totally defined. One theory is that the
relative immaturity of the sympathetic nervous system would make children's
vasomotor tone less dependent on this system and that capacitance veins in lower
extremities are small and send little blood flow for this region3,9-15,18,35-37.

Oberlander et al.37
have prospectively observed autonomic changes in a group of neonates submitted
to spinal anesthesia with a high sensory block level. There has been hemodynamic
stability and the authors concluded that spinal anesthesia would decrease heart
vagal tone, thus compensating any sympathetic block-induced effect and maintaining
cardiovascular stability.

Respiratory

Pascuci et al.38 have
investigated the effects of spinal anesthesia with high thoracic sensory block
in chest wall displacements of seven pre-term neonates submitted to inguinal
herniorrhaphy. The inspiratory movement of the costal grid was decreased in
6 children and 4 of them presented paradoxical rib movements. However, there
have been no heart rate or oxygen peripheral saturation changes.

On the other hand, other authors
have reported respiratory failure or apnea when sensory and motor block levels
were above the first thoracic dermatome (T1), with the need for ventilatory
assistance until blockade regression12,39-41.

O'Higashi et al.42
have induced spinal block in 8 children with progressive muscular dystrophy
and 2 patients presented with respiratory failure and bronchospasm due to the
high level of the blockade. In adults, bronchospasms due to high spinal block
are still controversial. It has been suggested that airways reactivity may increase
due to the decrease in circulating catecholamines as a consequence of this anesthetic
technique19,43,44.

Rice et al.45 have
investigated transcutaneous CO2 and oxygen peripheral saturation
and have observed no changes in such parameters in 15 high risk neonates submitted
to spinal anesthesia with sensory block in T4.

COMPLICATIONS

Complications in children are lower
than in adults46.

Several authors have referred a
relative cardiovascular stability, even with blockades at T4. In
children above 8 years of age, there is a decrease in blood pressure and bradycardia,
as in adults.

Some respiratory failures were
described with the need for ventilatory assistance, especially in spinal blocks
close to T1 41,42.

Giaufré et al.46,
in 1996, have published a study on regional anesthesia epidemiology and morbidity
in children and spinal anesthesia had a very low morbidity rate. From 502 patients,
there was only one complication caused by intravascular injection and without
clinical effects.

Post-dural puncture headache may
be present in children. Kokki et al.47 have shown that this adverse
effect would be detected in younger children, although being rare in children
under 10 years of age. These authors have reported post-dural puncture headache
and symptoms such as nausea, vertigo and photophobia in 12% of children under
10 years of age, and in 13% of children above this age. No child needed epidural
blood patch. The incidence of post-dural puncture headache was not changed with
the use of Quincke or Whitacre needles and was 15% and 9%, respectively48.

In this same study, authors have
shown that the risk for developing such complication was not age-dependent.
Eight out of eleven patients with post-dural puncture headache were below 10
years of age and the youngest patient with such complication was 23 months old48.

Other complaints, such as lumbar
pain and transient radicular irritation were also found within this age bracket47,48.

INDICATIONS AND COUNTERINDICATIONS

There is in the literature a broad
indication of spinal anesthesia for surgeries going from lower limbs up to ductus
arteriosus correction and pneumectomy.

Other applications of this technique
are limited by anesthesia duration, which averages 90 minutes. However, the
technique seems to be especially attractive for neonates with history of prematutiry
apnea and pulmonary bronchodysplasia, due to the risk of developing postoperative
respiratory complications and/or apnea.

Neonatal apnea is more frequent
in pre-term neonates with post-conceptual age under 44 weeks, although the absence
of such event does not rule out its postoperative incidence in this group of
patients49. Surgical procedures in this group at risk for neonatal
apnea are very frequent, especially inguinal herniorrhaphies. The observation
that general anesthesia or sedation would increase the incidence of postoperative
apnea has paved the way for the search for other anesthetic techniques. Some
authors have shown the absence of postoperative apnea in pre-term neonates submitted
to spinal anesthesia without simultaneous sedation11. However, Tobias
et al.26 have described bradycardia and apnea in two pre-term babies
who received spinal anesthesia alone without sedation or anesthetic supplementation.
The exact mechanism of such events was not detected, but these side-effects
were reverted at the end of the spinal block.

So, this group of children should
not be submitted to outpatient anesthesia because they should be followed up
for 24 hours after any anesthetic procedure, regardless of the technique.

Absolute counterindications are
the same as for adults and include patients or relatives refusal, major and
non corrected hypovolemia, blood coagulation abnormalities, needle insertion
site infection, sepsis and changes in intracranial compliance with the increase
in intracranial pressure13.

CONCLUSIONS

Spinal anesthesia in children has
gained a new breath. In some cases it may be an alternative for general anesthesia.
It is less expensive as compared to general anesthesia, promotes good muscle
relaxation and postoperative analgesia if associated to other drugs and the
incidence of adverse effects seems to be low.

However, it must be highlighted
that the risk/benefit ratio of any anesthetic technique should be the major
guide for the choice.